Spark plasma sintered α-SiC/β-SiC composites derived from polymer precursors: Microstructure and mechanical properties

Dense α-SiC-based composite ceramics reinforced by in situ formed β-SiC were rapidly fabricated at low temperatures by spark plasma sintering (SPS) using α-SiC/polycarbosilane (PCS) hybrid powders. The effect of PCS content on the microstructure and mechanical properties of the composite ceramics was investigated. The results show that the direct addition of non-crosslinked, non-pyrolyzed PCS effectively refines grain and improves overall mechanical performance. The sample containing 5 wt% PCS exhibited the most favorable properties, achieving a high relative density (99.2 %), Vickers hardness (27.5 ± 0.4 GPa), bending strength (526.1 ± 34.8 MPa), and fracture toughness (7.7 ± 0.6 MPa m^1/2) at a sintering temperature of 1750 °C, with a refined grains size of approximately 0.6 μm. With increasing PCS content, the fracture mode gradually shifted from predominantly transgranular to intergranular fracture. The main toughening mechanisms include microcrack toughening, second-phase toughening, and fine-grain toughening. A simplified, short-cycle, and low-temperature densification strategy for fabricating high-performance SiC ceramics was developed through precursor-assisted structural design.